1. Field of the Invention
This invention relates to the field of processes for manufacturing a whole wheat food product such as a breakfast cereal, and in particular, to such processes in which a cooked whole wheat must undergo tempering prior to shaping and baking.
2. Description of the Prior Art
Starch is the major component of whole wheat, present in most types of wheats at levels in excess of 50% by weight. Since it is the major constituent, changes in its chemical and physical properties will greatly affect the properties of the whole wheat berry. Wheat starch is composed of two polysaccharides which are polymers of D-glucose. One, amylose, is a linear polymer and the other, amylopectin, is a branched, bushlike polymer. These two polysaccharides in an approximate proportion of 1:3, amylose:amylopectin, occur naturally in wheat endosperm in the form of large lenticular granules. Where the adjacent linear molecules or the outer branches of the branched molecules are packed in a parallel arrangement, they are believed to be held together by hydrogen bonds forming crystalline regions. Between crystalline regions are loosely packed amorphous material, easily accessible to water. Gelatinization is the term most frequently applied to the sequence of changes which occur when starch is heated in water, i.e., cooked. The onset of gelatinization occurs with the sudden swelling of the starch granules at about 60.degree. C. As the temperature increases, the granules continue to take up water and expand considerably although still retaining their entity because of residual bonding in the crystalline regions. However, many of the bonds in the crystalline regions are broken. When the heated, gelatinized starch granules are allowed to cool, intermolecular bonds form both within and between swollen starch granules and their fragments. This return to a crystalline structure, which is not that of the original starch granules has been termed retrogradation. In the manufacture of a whole wheat food product such as shredded wheat, whole wheat is cooked sufficiently to gelatinize the starch. If shredding is attempted shortly after cooking, i.e., before the gelatinized wheat has cooled to provide a sufficient degree of retrogradation, or tempering, one obtains at best short non-continuous strands and/or strands which are tough, curly or suffer from some other physical or textural disadvantage. This result is primarily due to the amorphous sponge-like nature of freshly gelatinized starch. However, if the freshly cooked whole wheat is permitted to cool for a certain period, retrogradation will occur with a consequent increase in the rigidity of the starch polysaccharides. With sufficient retrogradation of the starch, shredding or other similar shaping operation will provide good shreds.
In known and conventional processes for manufacturing a whole wheat food product, tempering of the cooked whole wheat is commonly carried out by holding the wheat at ambient pressure and temperature, e.g., from about 15.degree. to 30.degree. C., for a period of from 8 to 28 hours. As a result of the tempering, the grain attains a uniform temperature and moisture content and the starch content thereof is sufficiently retrograded to permit effective shaping of the cooked wheat. Such relatively lengthy tempering periods require substantial storage facilities and result in a more time-consuming, complex and labor-intensive manufacturing cycle.
While it is recognized that the rate of ageing of concentrated wheat starch gels is increased at reduced temperature (McIver et al., "Kinetic Study of the Retrogradation of Gelatinised Starch", J. Sci. Fd. Agric., October, 1968, Vol. 19, pp. 560-563; K. H. Colwell et al., "Effect of Storage Temperature on the Ageing of Concentrated Wheat Starch Gels", J. Sci. Fd. Agric., September, 1969, Vol. 20, pp. 550-555), heretofore there has been no recognition or appreciation that the tempering of cooked wheat is accelerated within a certain range of chilling temperature.
U.S. Pat. No. 1,372,842 to Sutherland describes cooling flour to 0.degree. C. or below, preferably after a heating step in which the flour is quickly heated up to 75.degree. C., thereby increasing the yield of bread prepared from such flour. U.S. Pat. No. 1,670,016 to Bartmann calls for alternate heating and cooling of wheat from 100.degree. C. to 0.degree. C. in a very short time for the purpose of paralyzing or killing the germ. Neither of these patents is concerned with the tempering of cooked wheat to be used in the manufacture ofbreakfast cereal.